On Thu, 30 Sep 2004 18:05:58 EDT, ARDUJENSKI@aol.com wrote:
>As you aptly pointed out in most cases RF problems are
>generally site specific relating to type of antenna/feed system, station
>grounding, etc.
RFI problems have two parts. Both have to be present for there to be problems.
1) Something has to cause the RF to be in the shack. This is entirely related
to the
antenna system -- the antenna itself, the tuner, any counterpoise, etc. If you
have use a
long wire antenna that ends in the shack, there WILL be RF in the shack.
Various forms
of mismatch can also put it there. When there is RF in your shack, it will
induce current
onto the wiring in your shack by antenna action (for example, your mic cable,
the cable
connecting to to your computer, etc.) Repeat after me -- "we say "mic cable,"
mother
nature says "antenna."
2) Something has to couple it into parts of the radio where it doesn't belong.
The most
common way this happens is incorrectly terminated shield wiring on mic inputs,
loudspeaker outputs, serial control lines, etc. The correct place to connect
the shield is
the chassis. Connecting it anywhere else (like the circuit board) couples any
current
flowing on the shield into the radio. Every TenTec radio I have owned does it
wrong, and
so does most other ham gear. If you don't believe me, open up you radio and
look at the
RCA connectors -- they go to the circuit board, not the chassis. TILT!
In the pro audio world, this is known as "the pin 1 problem" because pin 1 of
the XLR
connector used for pro audio is the designated shield contact. Lots of pro
gear,
including nearly all everything manufactured before about 1999, has pin 1
problems.
We've been fixing our problems. It's time for the ham radio manufacturers to do
the
same.
Jim Brown K9YC
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